Aerial drones, especially the micro, multi-rotor class with hovering capability, are fast emerging as a powerful new class of mobile sensing systems with a rich sensory gamut neatly combined with on-board communication and computing elements, and mobile agility regardless of the terrain and space (indoor/outdoor) constraints. They, also referred to as micro aerial vehicles (MAVs) are increasingly finding their usage across a wide range of applications ranging from industrial (e.g., infrastructure inspection of near-inaccessible areas such as civil structure or machinery/asset at high elevation, utility pipeline or overhead cable inspection over very long distances, etc.,) to humanitarian (e.g., search and rescue, emergency response, etc.,) sectors.
Vision is the most prominent mode of sensing in MAVs. Compared to other spatially rich sensors such as sonar and laser range finders (that are commonly used in terrestrial vehicles), vision sensors require comparatively lower energy to interrogate the environment and for a comparable mass, they can gather richer information and span wider fields of view. However, the MAVs become unusable in camera obstructed, occluded, low-light conditions, or in scenarios that offer profound non-visual clues (such as auditory acoustics).